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The protein complex composed of actin and myosin, contractile proteins, is sometimes referred to as actomyosin.In striated skeletal and cardiac muscle, the actin and myosin filaments each have a specific and constant length in the order of a few micrometers, far less than the length of the elongated muscle cell (up to several centimeters in some skeletal muscle cells). [5]
A myofibril (also known as a muscle fibril or sarcostyle) [1] is a basic rod-like organelle of a muscle cell. [2] Skeletal muscles are composed of long, tubular cells known as muscle fibers, and these cells contain many chains of myofibrils. [3] Each myofibril has a diameter of 1–2 micrometres. [3]
The third type of myofilament is an elastic filament composed of titin, a very large protein. In striations of muscle bands , myosin forms the dark filaments that make up the A band . Thin filaments of actin are the light filaments that make up the I band .
In biology, a motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron's axon terminals, including the neuromuscular junctions between the neuron and the fibres. [1]
Striated muscle tissue is a muscle tissue that features repeating functional units called sarcomeres.The presence of sarcomeres manifests as a series of bands visible along the muscle fibers, which is responsible for the striated appearance observed in microscopic images of this tissue.
Myofibroblasts usually stain for the intermediate filament vimentin, which is a general mesenchymal marker, α-smooth muscle actin (human gene = ACTA2), and for palladin, which is a cytoskeletal actin scaffold protein.
The dense bodies and intermediate filaments are networked through the sarcoplasm, which cause the muscle fiber to contract. Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle.
The sarcolemma (sarco (from sarx) from Greek; flesh, and lemma from Greek; sheath), also called the myolemma, is the cell membrane surrounding a skeletal muscle fibre or a cardiomyocyte.